The present invention relates, in general, to plywood itself. More specifically, it relates to improved and novel stratified structure of plywood composed of veneers any of which are short for any given desired lengths of plywood panel.
In a plywood panel which is composed of any desired plural number of plies of veneer glued together into a stratified form, its component veneers include uppermost and lowermost plies of the plywood panel which are usually referred to as the face veneer and back veneer, respectively, and thus constitute the opposite top and bottom faces of the panel. For the sake of reference simplicity, these face and back may be referred to collectively merely as the "face veneers" simply because the face and the back are distinguished from each other especially when the plywood is irreversible for any specific purpose of application. Other component plies of veneer interposed between the faces and therefore constitute the inner layer of plywood include those veneers which have grain running substantially in the same direction as the faces and are referred to as the "longitudinal veneer", and those veneers whose grain runs substantially at a right angle with respect to the grain of the faces and which are referred to as the crossband or "cross veneer". In the manufacture of plywood, it is a usual practice to employ veneers of lower grade for the latter longitudinal and cross veneers because they are arranged so as to form the invisible inner layer of plywood panel.
It has been known heretofore, in manufacturing plywood with any desired lengths that veneer short for desired lengths is end-jointed by any of the joint forms such as butt joint, scarf joint, finger joint, etc., and the plies of such veneer are arranged and then glued together thereby to assemble a plywood panel of the desired lengths. However, any of these conventional joints have presented a crucial disadvantage or drawback in that the plywood thus obtained is inferior to non-joint plywood in strength, and therefore plywood containing such connection joints therein lacks product reliability in respect of strength thereof. Though it is technically possible to provide sufficiently strong joints in plywood, this would inevitably degrade the yield involved in plywood production, thereby inviting an increase of production cost. In this way, it is safe to say that plywood with joints has been manufactured heretofore at the sacrifice of strength that is an important property of plywood. As a result, the scope of use of such plywood has been limited to some particular applications which do not call for strength requirement.